The repair of tendons or ligaments is a challenging and complication-prone area of surgery. Over the past 40 years, improvements in the art of tendon and ligament repair have focused primarily on suture techniques used to repair tendons and ligaments. Tendons can sustain high tensile forces resulting from muscle contraction, yet are flexible enough to bend around bony surfaces and deflect beneath retinacula to change the final direction of muscle pull. Tendons attach muscle to bone and transmit tensile loads from muscle to bone, thereby producing joint movement. Ligaments attach bone to bone and can flex to allow natural movement of the bones that they attach, but are strong and inextensible so as to offer suitable resistance to applied forces. Ligaments augment the mechanical stability of the joints.
Bundles of collagen fibers embedded in a connecting matrix, known as ground substance, provide the load carrying elements of natural tendons and ligaments. The tensile strength of tendons and ligaments is provided by the lengthwise parallel collagen fibers, which give them the ability to withstand high tensile loads. The arrangement of collagen fibers is nearly parallel in tendons, equipping them to withstand high unidirectional loads. The less parallel arrangement of the collagen fibers in ligaments allows these structures to sustain predominant tensile stresses in one direction and smaller stresses in other directions. The ground substance in both tendons and ligaments acts generally as a cementing matrix to hold the collagen fibers together.
Today, the most common methods of repairing torn, severed or otherwise damaged tendons involve approximating the severed ends of the tendons and suturing one side of the tendon to the other, thereby returning the tendon to its natural position. Most suture methods employ an internal suture with external knots distal and proximal to the laceration, or within the laceration. Most sutures typically include a continuous running external suture at the junction of the repair, known as an epitendinous suture, to approximate the tendon ends. Other methods of repairing a damaged tendon involve the placement of prosthetic material either within or around the tendon. Whether prosthetics are used or the repair is done using only sutures, both methods involve external sutures or knots which have the disadvantage of creating sites for the development of adhesions, the growth of cells around the foreign material, as a result of the body's natural healing process. The development of adhesions and the external foreign material promote increased work of flexion of the repaired tendons and ligaments. Increased risk of adhesions and increased work of flexion is exacerbated when the number of suture strands increases, or the amount of suture material or prosthetic material is increased, as is commonly done to affect a stronger repair.
The effectiveness of sutures depends upon many factors, including the techniques used to create the sutures. These techniques are difficult to master and very tedious to perform. The use of internal or external prosthetic splints also pose increased risk for the development of adhesions, and large slits that are created for the insertion of splints within the tendons create risk of structural damage to the internal blood supply, which may cause tissue degeneration.
Another problem of conventional tendon repair methods relates to the softening of the damaged tendon ends, which begins shortly after the damage or injury occurs and continues for approximately 12 days. This softening results in a weakening of the tendon fibers, which may contribute to the formation of a gap at the repair site during the early phases of tendon healing. It is believed that gaps form at the repair site due to a loss of purchase by the grasping portion of the suture at the tendon-suture interface. The grasping suture may even completely tear out, resulting in a failure of repair called “rake out.”
The ideal repair for a tendon or ligament is one which exhibits high strength, high flexibility, and the ability to join the ends of the tendon or ligament without any foreign material on the outside surface of the tendon or ligament. Current and past tendon or ligament repair techniques have concentrated on increasing the tensile strength of the repair by adding more structural components to the repair (for example, sleeves, splints, additional suture strands, additional knots). All of these techniques trade off between early tensile strength at the repair site and increased work of flexion and increased risk of adhesions or other problems. None of these techniques have utilized the physiological make up of the tendon to provide a stronger repair.
The attachment of tendons, ligaments, and other soft tissue to bone, such as in arthroscopic shoulder stabilization or rotator cuff repair, presents problems similar to those experienced in intra-tendon or intra-ligament repair. In this regard, simply suturing soft tissue to a bone anchor or using external soft tissue anchor members may not provide the necessary strength of repair. These techniques also promote the formation of adhesions on tendons ligaments, and other soft tissue and increase the work of flexion of the tendons and ligaments, as discussed above.
Finally, retrieval of soft tissue has also been a problematic area of repair surgery. Typically, a surgeon must use a small grasping tool with thin, movable jaws similar to needle-nose pliers to grasp the end of the soft tissue and pull and transfix it in an appropriate operating position. Unfortunately, gripping soft tissue in this manner often damages the tissue and makes the tissue less able to hold the epitendinous suture. These damaged ends will also form scar tissue or adhesions which further adversely affect the repair.
There is thus a need for tendon repair techniques and apparatus that utilize harness the intrinsic strength of soft tissue fibers, but allow the tendon to flex while moving. These repair apparatus should resist any gapping or rupture during immediate post-operative physical therapy, and reside in the interior of the soft tissue to reduce or possibly eliminate post-operative adhesions. The repair apparatus should also produce low work of flexion while gliding unhindered through the tendon sheaths. There is generally a need for soft tissue repair apparatus and methods that allow the patient to immediately begin active physical therapy without risking any tendon repair failure while minimizing or eliminating the need for sutures or other repair structure on the external surfaces of the soft tissue, thereby reducing the formation of adhesions. There is a further need for soft tissue-to-bone repair techniques and apparatus with at least some of these attributes. Finally, there is a need for a soft tissue retrieval device which also utilizes the inherent strength of the fibers and minimizes damage to the retrieved end of the soft tissue.